What is a history word starting with an o?

The civil war has been given many names: the war between the states, the war against northern aggression, the second american revolution, the lost cause, the war of the rebellion, the brothers' war, and the late unpleasantness. famous poet walt whitman called it the war of attempted secession. confederate general joseph johnston called it the war against the states. by whatever name, it was unquestionably the most important event in the life of the nation. which name do you feel best fits this war from the list above? maybe you have another name you think would be even better? give the name you feel fits this war best, and in a sentence or two, explain your reasoning.